1. Field of the Invention
This invention relates to a safety apparatus for an elevator which brakes the elevator when the speed of movement of the elevator reaches a prescribed critical speed.
2. Description of the Prior Art
FIGS. 24(a) and 24(b) are a front elevational view and a plan view, respectively, of a governor which is a conventional safety apparatus for an elevator. Referring to FIGS. 24(a) and 24(b), reference numeral 12 denotes a cage of the elevator, 13 a base of the elevator governor provided on the cage 12, and 14 an arm composed of two pairs of parallel links supported pivotally around fulcra 15 on the base 13. Reference numeral 16 denotes a pickup connected at two points to an end of the arm 14 for detecting a rapid speed of the elevator. The pickup 16 has a magnetic circuit composed of a pair of magnets 16a disposed in an opposing relationship to a fixed conductor 18 on the opposite sides of the fixed conductor 18, and a back yoke 16b for assuring a path for magnetic fluxes of the magnets 16a. Reference numeral 17 denotes a balance weight provided at the other end of the arm 14 in a balanced relationship with the pickup 16. It is to be noted that the governor is composed of the arm 14, fulcra 15 of the base, pickup 16 and balance weight 17. Reference numeral 19 denotes a spring which holds the arm 14 and converts a force (drag) acting upon the balance weight 17 into a displacement. Reference numeral 20a denotes a cage stopping switch, and this cage stopping switch 20a disconnects, by a displacement of the balance weight 17, a power supply for a winding machine or the like (not shown) for moving the elevator up and down. Reference numeral 21 denotes an emergency stopping operation bar, and this emergency stopping operation bar 21 activates an emergency stopping apparatus (brake apparatus (not shown)).
Operation of the governor which is a conventional safety apparatus for an elevator is described below.
The pickup 16 has a magnetic circuit composed of the magnets 16a and the back yoke 16b and produces a magnetic field perpendicular to the plane of the fixed conductor 18 located between the two magnets 16a. When the cage 12 moves up or down and the magnetic field moves in the fixed conductor 18, such eddy current as cancels a variation of the magnetic field is generated in the fixed conductor 18, and a force (magnetic drag) having a magnitude corresponding to the speed of the cage 12 and acting in a direction to resist the movement of the cage 12 is generated on the magnets 16a. It is to be noted that a relationship between the speed V of the cage 12 and the generated magnetic drag F1 is illustrated in FIG. 26. This magnetic drag F1 is converted into a displacement of the pickup 16 and the balance weight 17 in the upward or downward direction by the arm 14 and the springs 19 as seen in FIG. 25. It is to be noted that a relationship between the pickup displacement (balance weight displacement) Z and the spring force F2 is illustrated in FIG. 27, and a relationship between the speed V of the cage 12 and the pickup displacement (balance weight displacement) Z is illustrated in FIG. 28.
When the speed of downward movement of the cage 12 reaches a first over-speed (normally set to approximately to 1.3 times a rated speed) higher than a predetermined value, the magnets 16a are acted upon by an upward magnetic drag corresponding to the speed and displaces the balance weight 17 downwardly. Then, as a result of the displacement, the cage stopping switch 20a operates to disconnect the power supply to the elevator driving apparatus and the cage 12 stops. On the other hand, also when the speed of downward movement of the cage 12 reaches a second over-speed (normally set to approximately 1.4 times the rated speed) by some cause, the balance weight 17 is further displaced downwardly corresponding to the speed, and as a result of the displacement, the emergency stopping operation bar 21 moves to operate the emergency stopping apparatus (not shown) provided for the cage 12 so that the cage 12 is stopped suddenly.
It is to be noted that, in addition to the prior art described above, a technique similar to the present invention is disclosed in JP-A 5-147852 or JP-A 6-321454.
Since the conventional safety apparatus for an elevator is constructed in such a manner as described above, it has the following subjects.
(a) In the conventional safety apparatus for an elevator, since the magnetic drag generated by eddy current is low comparing with a force necessary to activate the emergency stop and, even when the speed of downward movement of the cage reaches the second over-speed, the displacement of the pickup is small, there is a subject in that it is difficult only for the magnetic drag to activate the emergency stop and the stability of operation is low. PA1 (b) In the conventional safety apparatus for an elevator, while a balance weight is provided such that it may be balanced with the pickup, since the balance weight is connected to the emergency stopping apparatus (brake apparatus) by the emergency stopping operation bar or a like member, the entire connected apparatus is not in a well-balanced state, and consequently, there is another subject in that the pickup is liable to be displaced by a force applied to the case such as vibrations of the case (when passengers get in or out), and consequently, a malfunction is likely to occur. PA1 (c) In the conventional safety apparatus for an elevator, since the pickup is mounted at an end of the arm and the balance weight is mounted at the other end of the arm to establish a well-balanced relationship, there is a further subject in that a downward force for canceling the emergency stop cannot be applied in an ordinary operation and, even if it is tried to cancel a situation that the emergency stopping apparatus bites in the guide rail after the emergency stopping apparatus operates, the emergency stopping apparatus does not restore its initial state readily. PA1 (d) In the conventional safety apparatus for an elevator, if the speed of the cage temporarily fluctuates oscillatorily to a large extent when passengers get in or out or when passengers in the cage move violently, then the displacement of the pickup exhibits a large amount, and there is a still further subject in that the safety apparatus is liable to malfunction. PA1 (e) In the conventional safety apparatus for an elevator, since the governor and the emergency stopping apparatus are disposed separately above and below the cage, there is a yet further subject in that the safety apparatus has a large size as a whole. PA1 (f) In the conventional safety apparatus for an elevator, upon operation inspection or checking when it is installed at the site or maintenance of it is performed, the cage must actually be moved to check the operation, and there is a yet further subject in that an inspection or checking is difficult and dangerous.